(1) Field of the Invention
The present invention relates generally to III-nitride semiconductors and more particularly to crucibles for growing III-nitride semiconductor substrates such as aluminum nitride (AlN). Use of the crucible of this invention may enable the growth of relatively large and high quality III-nitride single crystals.
(2) Background Information
Wide bandgap semiconductor devices, based on III-nitride semiconductors, are expected to find application in several opto-electronic technologies in the areas of short wavelength emission and detection. Aluminum nitride and high aluminum concentration alloys of aluminum nitride with gallium nitride and/or with indium nitride are potentially important III-nitride semiconductors for producing deep-UV light emitting diodes with potential applications including solid-state white lighting, sterilization and disinfectant devices, compact analytical devices for the biotechnology and pharmaceutical markets, bioagent detection systems, compact uv light sources for covert communication by the Department of Defense, and for short wavelength lasers for high density data storage. In addition, single-crystal substrates of aluminum nitride are attractive for the fabrication of III-nitride semiconductor, high power radio frequency, millimeter wave, and microwave devices needed for future wireless communication base stations and for Department of Defense applications. However, one of the factors limiting the maturation of aluminum nitride, and other III-nitride, technology has been the absence of high-quality bulk nitride substrates.
One promising method for the growth of aluminum nitride single crystals for such substrates is the sublimation-recondensation technique first developed by Slack and McNelly (“Growth of High Purity AlN Crystals”, J. Cryst. Growth 34, 263 (1976) and “AlN Single Crystals”, J. Cryst. Growth 42, 560 (1977)), both of which are fully incorporated by reference herein. However, one of the drawbacks that limited the maximum size of the crystals was the development of leaks in the tungsten crucibles, which ultimately lead to the failure thereof, through which aluminum gas may escape. The development of crucibles that substantially eliminate this problem may provide for the growth of relatively large aluminum nitride single crystals. The need for improved crucibles for the growth of aluminum nitride single crystals has also been published, subsequent to the priority date of embodiments of the present invention, by other groups: “Properties of Crucible Materials for Bulk Growth of AlN,” G. A. Slack, J. Whitlock, K. Morgan, and L. J. Schowalter, Materials Research Society Proc. Vol. 798, p. Y10.74.1 (2004); “Crucible Selection in AlN Bulk Crystal Growth,” R. Dalmau, B. Raghothamachar, M. Dudley, R. Schlesser, and Z. Sitar, Materials Research Society Proc. Vol. 798, p. Y2.9.1 (2004); and “Sublimation Growth of Bulk AlN Crystals: Materials Compatibility and Crystal Quality,” B. M. Epelbaum, D. Hofmann, M. Bickermann, A. Winnacker, Mater. Sci. Forum 389–393, 1445 (2002).
Therefore there exists a need for an improved crucible for growth of III-nitride.